The invention relates to devices that fix soft tissue to support structures, particularly devices that fix soft tissue grafts within bone tunnels.
In certain types of surgical procedures, soft tissue grafts must be fixed within a bone tunnel. For example, in anterior cruciate ligament (ACL) replacement surgery, a ligament graft is harvested from the patient or from a donor, and implanted within the knee by securing one end within a bone tunnel drilled through the tibia, and the other end within a bone tunnel drilled through the femur. Several ACL reconstructive techniques are described in Rosenberg, U.S. Pat. No. 5,139,520, which is incorporated herein by reference.
Referring to FIG. 1, a ligament graft 10 can be fixed within a bone tunnel using a bone screw 12. Graft 10 is made from e.g., a single or double long strip of soft tissue. To implant graft 10, the middle of the strip (not shown) is first passed in a distal direction through a first tunnel 14 in the tibia into a second tunnel 18 in the femur, and then attached to the femur tunnel (or attached to bone adjacent the femur tunnel) with a femur fixation device (not shown). Two approximately equal length segments 19a, 19b of the graft extend proximally from the attached middle portion through tunnels 18 and 14. The two ends 20a, 20b of segments 19a, 19b terminate proximal to tibial tunnel 14. Segments 19a and 19b of the graft are then fixed within tibial tunnel 14 by inserting bone screw 12 between the two segments, such that shaft 22 of the screw presses the segments against internal wall 24 of tunnel 14.
In attaching soft tissue within a bone tunnel using a bone screw, it is important that the tissue be rigidly fixed within the tunnel to prevent slippage. When the bone involved is relatively soft (less calcified), a common problem in elderly patients, screws may not adequately fix the graft to the bone.
In general, in one aspect, the invention features a sheath for an implantable fixation device. The sheath has a flexible body with a relieved wall, and the body defines an interior sized and shaped to receive the fixation device.
Embodiments of this aspect of the invention may include one or more of the following features.
The body defines a tube that is sized and shaped to receive the fixation device. For example, the device is sized and shaped to snugly receive a shaft of a bone screw, and the device""s body is conformable to the bone screw shaft. Alternatively, the interior can be sized and shaped to receive both the shaft of a bone screw and a soft tissue graft.
The body includes two open, generally circular ends, or an open end and a closed end. An external loop is attached to the exterior of the body.
Rather than a single tube, the body can include a second tube attached to the first tube, the second tube being sized and shaped to receive a portion of a soft tissue graft. Alternatively, the body can include a plurality of generally parallel tubes arranged to form a ring, at least some of the tubes being sized and shaped to receive a portion of the soft tissue graft. The ring defines a central cavity between the tubes that is sized and shaped to receive the fixation device.
The body is made from a bioabsorbable material, such as hydroxyapatite, polylactic acid, or polylactic and glycolic acid, and the body is integrally formed.
The body""s wall is perforated, e.g., the wall defines a plurality of holes therethrough. For example, the body is made from strands woven into a mesh structure, and the holes are the spaces between the mesh strands. A major portion of the wall is open. The wall""s thickness is less than about 0.3 mm, and its exterior surface is roughened.
The device further includes a therapeutic agent in contact with the body, such as an osteoinductive agent or a growth factor. The agent is, e.g., disposed on at least a portion of an exterior surface of the body, or integrated into a material that forms the body.
The sheath can also include a washer attached to a proximal end of the body. An upper surface of the washer has a plurality of teeth for gripping bone.
In another aspect, the invention features a combination of the sheath and a fixation device.
Embodiments of this aspect of the invention may include one or more of the following features.
The fixation device is a bone screw that has a shaft sized and shaped to fit within (e.g., snugly within) the interior of the sheath. The screw""s threads are rounded.
In another aspect, the invention features a sheath for an implantable fixation device that includes at least three generally parallel tubes arranged to form a ring. The ring defines a central cavity between the tubes that is sized and shaped to receive the fixation device.
Embodiments of this aspect of the invention may include one or more of the following features.
The central cavity includes a bore that is coextensive with the tubes. The ring of tubes includes, e.g., 3, 4, 5, 6, 7, or 8 tubes, and the sheath includes an external sleeve that surrounds the tubes. The tubes are flexible, and at least some of the tubes are sized and shaped to receive a portion of the soft tissue graft. At least some of the tubes are perforated. For example, in one embodiment, all the tubes have a mesh structure, and the ring of tubes is integrally formed.
In another aspect, the invention features a method of fixing soft tissue within a bone tunnel. The method includes: (a) placing both the soft tissue and a flexible, relieved, tube-shaped sheath within the bone tunnel, such that the sheath at least partly surrounds the soft tissue; and (b) positioning a fixation device within the sheath to press the soft tissue against an interior wall of the sheath, and to press the sheath against a wall of the bone tunnel, thereby fixing the soft tissue within the bone tunnel.
Embodiments of this aspect of the invention may include one or more of the following features.
The placing step includes first passing the soft tissue through the sheath, and then inserting the sheath into the bone tunnel. Alternatively, the placing step includes first inserting the sheath into the bone tunnel, and then locating the soft tissue within the bone tunnel such that the soft tissue passes through the sheath. The sheath""s body has a mesh structure, and a therapeutic agent is in contact with the body.
The fixation device is a bone screw that has a shaft, and the positioning step includes positioning the shaft within the sheath. The soft tissue is a ligament graft.
In another aspect, the positioning step of the method includes positioning a fixation device within the bone tunnel adjacent an exterior surface of the sheath to compress the soft tissue within the sheath and to press the exterior surface of the sheath against a wall of the bone tunnel, thereby fixing the soft tissue within the bone tunnel.
In another aspect, the invention features a method of fixing soft tissue within a bone tunnel that includes: (a) placing the soft tissue within the bone tunnel; (b) positioning a fixation device within an interior of a flexible, relieved, tube-shaped sheath; and (c) inserting the fixation device and the sheath into the bone tunnel to compress the soft tissue between an exterior surface of the sheath and a wall of the bone tunnel, thereby is fixing the soft tissue within the bone tunnel.
In another aspect, the invention features a method of fixing soft tissue within a bone tunnel that includes: (a) placing the soft tissue within the bone tunnel; (b) positioning a flexible, relieved, tube-shaped sheath within the bone tunnel adjacent the soft tissue; and (c) inserting a fixation device into an interior of the sheath to compress the soft tissue between an exterior surface of the sheath and a wall of the bone tunnel, thereby fixing the soft tissue within the bone tunnel.
In another aspect, the invention features a method of fixing soft tissue within a bone tunnel that includes: (a) inserting a sheath into the bone tunnel, the sheath having at least three generally parallel tubes arranged to form a ring, the ring defining a central cavity between the tubes; (b) passing segments of the soft tissue through at least two of the tubes; and (c) positioning a fixation device within the central cavity of the ring to compress the tubes between the fixation device and a wall of the bone tunnel, and to compress the soft tissue segments within their respective tubes, thereby fixing the soft tissue within the bone tunnel.
Embodiments of this aspect of the invention may include one or more of the following features.
The passing step is performed prior to inserting the sheath into the bone tunnel. The sheath has exactly four tubes arranged to form the ring, and the passing step includes passing segments of the soft tissue through each of the four tubes. The fixation device is a bone screw having a shaft, and the positioning step includes positioning the shaft within the central portion of the ring.
In another aspect, the invention features a method of fixing soft tissue within a bone tunnel that includes: (a) inserting a sheath into the bone tunnel, the sheath having two generally parallel tubes; (b) passing a portion of the soft tissue through a first of the two tubes; and (c) positioning a fixation device within the second of the two tubes to compress the first tube between the fixation device and a wall of the bone tunnel, and to compress the portion of the soft tissue within the first tube, thereby fixing the soft tissue within the bone tunnel.
The invention may include one or more of the following advantages.
The flexibility and thinness of certain embodiments of the sheath allows the sheath to conform, e.g., to the shape of the fixation device, or to the shape of a bone tunnel.
In certain embodiments, the sheath protects the soft tissue graft from laceration or cutting by threads of a fixation screw, and reduces twisting of the graft upon insertion of a screw.
The relief in the sheath, e.g., perforations in a wall of the sheath, allows in situ contact between a soft tissue graft and the wall of a bone tunnel, promoting development of Sharpy-like fibers and permanent attachment of the soft tissue to the bone.
Therapeutic agents, such as osteoinductors or growth factors, can be disposed on or embedded into the material of the sheath, allowing delivery of the agent directly to the site of fixation.
Other embodiments and advantages of the invention will be apparent from the following description and from the claims.